This invention relates to the froth flotation of coal-containing ashes, coal sludge or coal-containing residues to recover coal containing a lower percentage of impurities. In particular, this invention relates to the use of an aromatic polycyclic, hydrocarbon compound bearing at least one nuclear sulfonic acid or sulfonate moiety as a froth promoter for the flotation of finely-divided coal in the presence of a conventional frother.
The natural process of "coalification" inherently deposits some non-combustible mineral matter in association with the combustible carbonaceous solids. Large fragments of non-combustible material can be removed by screening or other gravity concentration techniques, but other cleaning methods more efficiently remove fine material intimately associated with the carbonaceous solids. Froth flotation of coal is used in the art to beneficiate finely-divided raw coal. Bituminous coals generally possess a natural hydrophobicity, which results in the coal being floatable in the presence of a frother, such as methyl isobutyl carbinol, desirably with a relatively mild collector, such as kerosene. Anthracite coals, as well as coals of all ranks in which the surface has been at least partially oxidized, are less amenable to flotation, resulting in the loss of significant amounts of combustible material with the tail fraction from the flotation.